1. Field of the Invention
The present invention relates to a semiconductor device including an oxide semiconductor and a manufacturing method thereof.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electrooptic device, a semiconductor circuit, and electronic equipment are all included in the category of semiconductor devices.
2. Description of the Related Art
Transistors using a semiconductor thin film which is formed over a substrate having an insulating surface are widely used in electronic devices such as integrated circuits (ICs) and image display devices (also simply referred to as display devices). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to such a transistor. In recent years, an oxide semiconductor has attracted attention.
Examples of such a transistor include a transistor in which zinc oxide (ZnO) is used as an oxide semiconductor and a transistor in which InGaO3(ZnO), is used as an oxide semiconductor. A technique in which a switching element, such as a transistor, in which a channel formation region is formed in an oxide semiconductor film is used for manufacturing an active matrix display device has also been developed.
Patent Document 1 discloses a three-layer structure in which a first multi-component oxide semiconductor layer is provided over a substrate, a one-component oxide semiconductor layer is stacked over the first multi-component oxide semiconductor layer, and a second multi-component oxide semiconductor layer is stacked over the one-component oxide semiconductor layer.
Non-Patent Document 1 discloses a transistor including a stack of oxide semiconductors.